Powered device classification in a wired data telecommunications network

ABSTRACT

In a wired data telecommunication network power sourcing equipment (PSE) coupled to a powered device (PD) carries out an inline power discovery process to verify that the PD is adapted to receive inline power, then a plurality of classification cycles are carried out to convey a series of inline power classes back to the PSE. The series of inline power classes may all be the same, in which case the PD is legacy equipment and is adapted to receive the power level corresponding to that class. If they are not all the same, information is thus conveyed to the PSE which may, for example, correspond to a specific power level to be applied or to other information.

STATEMENT OF RELATED CASES

This patent may be considered to be related to commonly owned U.S.patent application Ser. No. 10/961,864 filed on Oct. 7, 2004 andentitled “Bidirectional Inline Power Port” in the names of inventorsDaniel Biederman, Kenneth Coley and Frederick R. Schindler (AttorneyDocket No. CISCO-8799).

This patent may also be considered to be related to commonly owned U.S.patent application Ser. No. 10/961,243 filed on Oct. 7, 2004 andentitled “Redundant Power and Data Over A Wired Data TelecommunicationsNetwork” in the names of inventors Daniel Biederman, Kenneth Coley andFrederick R. Schindler (Attorney Docket No. CISCO-8800).

This patent may also be considered to be related to commonly owned U.S.patent application Ser. No. 10/961,904 filed on Oct. 7, 2004 andentitled “Inline Power—Based Common Mode Communications in a Wired DataTelecommunications Network” in the names of inventors Roger A. Karam,Frederick R. Schindler and Wael William Diab (Attorney Docket No.CISCO-9057).

This patent may also be considered to be related to commonly owned U.S.patent application Ser. No. 10/961,865 filed on Oct. 7, 2004 andentitled “Automatic System for Power and Data Redundancy in a Wired DataTelecommunications Network” in the names of inventors Roger A. Karam andLuca Cafiero (Attorney Docket No. CISCO-9068).

This patent may also be considered to be related to commonly owned U.S.patent application Ser. No. 10/___,___ filed on Nov. XXX, 2004 andentitled “Power Management for Serial-Powered Device Connections” in thename of inventor Roger A. Karam (Attorney Docket No. CISCO-9104).

This patent may also be considered to be related to commonly owned U.S.patent application Ser. No. 10/___,___ filed on Nov. XXX, 2004 andentitled “Redundant Power and Data In A Wired Data TelecommunicationsNetwork” in the names of inventors Roger A. Karam and Luca Cafiero(Attorney Docket No. CISCO-9105).

This patent may also be considered to be related to commonly owned U.S.patent application Ser. No. 10/___,___ filed on Nov. XXX, 2004 andentitled “Power and Data Redundancy in a Single Wiring Closet” in thenames of inventors Roger A. Karam and Luca Cafiero (Attorney Docket No.CISCO-9106).

This patent may also be considered to be related to commonly owned U.S.patent application Ser. No. 10/___,___ filed on Nov. 3, 2004 andentitled “Current Imbalance Compensation for Magnetics in a Wired DataTelecommunications Network” in the names of inventors Roger A. Karam andJohn F. Wakerly (Attorney Docket No. CISCO-9581).

This patent may also be considered to be related to commonly owned U.S.patent application Ser. No. 10/___,___ filed Jul. 15, 2004 and entitled“Improved Power Delivery over Ethernet Cable” in the names of inventorsWael William Diab and Frederick R. Schindler (Attorney Docket No.CPOL-385465).

This patent may also be considered to be related to commonly owned U.S.Pat, No. 6,541,878 entitled “Integrated RJ-45 Magnetics with PhantomPower Provision” in the name of inventor Wael William Diab.

This patent may also be considered to be related to commonly owned U.S.patent application Ser. No. 10/___,___ filed Jul. 20, 2004 and entitled“Methods and Apparatus for Provisioning Phantom Power to Remote Devices”in the name of inventors Wael William Diab and Frederick R. Schindler(Attorney Docket No. CPOL-326694).

FIELD OF THE INVENTION

The present invention relates generally to networking equipment which ispowered by and/or powers other networking equipment over wired datatelecommunications network connections.

BACKGROUND OF THE INVENTION

Inline Power (also known as Power over Ethernet and PoE) is a technologyfor providing electrical power over a wired data telecommunicationsnetwork (such as, for example, the well-known Ethernet) from powersource equipment (PSE) to a powered device (PD) over a link section. Thepower may be injected by an endpoint PSE at one end of the link sectionor by a midspan PSE along a midspan of a link section that is distinctlyseparate from and between the media dependent interfaces (MDIs) to whichthe ends of the link section are electrically and physically coupled.

PoE is defined in the IEEE (The Institute of Electrical and ElectronicsEngineers, Inc.) Standard Std 802.3af-2003 published 18 Jun. 2003 andentitled “IEEE Standard for Information technology—Telecommunicationsand information exchange between systems—Local and metropolitan areanetworks—Specific requirements: Part 3 Carrier Sense Multiple Accesswith Collision Detection (CSMA/CD) Access Method and Physical LayerSpecifications: Amendment: Data Terminal Equipment (DTE) Power via MediaDependent Interface (MDI)” (herein referred to as the “IEEE 802.3afstandard”). The IEEE 802.3af standard is a globally applicable standardfor combining the transmission and reception (collectively:“transceiving”) of Ethernet packets with the transmission and receptionof DC-based power over the same set of wires in a single Ethernet cable.It is contemplated that Inline Power will power such PDs as InternetProtocol (IP) telephones, surveillance cameras, switching and hubequipment for the telecommunications network, biomedical sensorequipment used for identification purposes, other biomedical equipment,radio frequency identification (RFID) card and tag readers, securitycard readers, various types of sensors and data acquisition equipment,fire and life-safety equipment in buildings, and the like. The power isdirect current, floating 48 Volt power currently available at a range ofpower levels from about 4 watts to about 15 watts in accordance with thestandard. There are mechanisms within the IEEE 802.3af standard toallocate a requested amount of power. Other proprietary schemes alsoexist to provide a finer and more sophisticated allocation of power thanthat provided by the IEEE 802.3af standard while still providing basiccompliance with the standard. As the standard evolves, additional powermay also become available. Conventional 8-conductor type RG-45connectors (male or female, as appropriate) are typically used on bothends of all Ethernet connections. They are wired as defined in the IEEE802.3af standard.

FIGS. 1A, 1B and 1C are electrical schematic diagrams of three differentvariants of PoE as contemplated by the IEEE 802.3af standard. In FIG. 1Aa data telecommunications network 10 a comprises a switch or hub 12 awith integral power sourcing equipment (PSE) 14 a. Power from the PSE 14a is injected on the two data carrying Ethernet twisted pairs 16 aa and16 ab via center-tapped transformers 18 aa and 18 ab. Non-data carryingEthernet twisted pairs 16 ac and 16 ad are unused in this variant. Thepower from data carrying Ethernet twisted pairs 16 aa and 16 ab isconducted from center-tapped transformers 20 aa and 20 ab to powereddevice (PD) 22 a for use thereby as shown. In FIG. 1B a datatelecommunications network 10 b comprises a switch or hub 12 b withintegral power sourcing equipment (PSE) 14 b. Power from the PSE 14 b isinjected on the two non-data carrying Ethernet twisted pairs 16 bc and16 bd. Data carrying Ethernet twisted pairs 16 ba and 16 bb are unusedin this variant for power transfer. The power from non-data carryingEthernet twisted pairs 16 bc and 16 bd is conducted to powered device(PD) 22 b for use thereby as shown. In FIG. 1C a data telecommunicationsnetwork 10 c comprises a switch or hub 12 c without integral powersourcing equipment (PSE). Midspan power insertion equipment 24 simplypasses the data signals on the two data carrying Ethernet twisted pairs16 ca-1 and 16 cb-1 to corresponding data carrying Ethernet twistedpairs 16 ca-2 and 16 cb-2. Power from the PSE 14 c located in theMidspan power insertion equipment 24 is injected on the two non-datacarrying Ethernet twisted pairs 16 cc-2 and 16 cd-2 as shown. The powerfrom non-data carrying Ethernet twisted pairs 16 cc-2 and 16 cd-2 isconducted to powered device (PD) 22 c for use thereby as shown. Notethat powered end stations 26 a, 26 b and 26 c are all the same so thatthey can achieve compatibility with each of the previously describedvariants.

Turning now to FIGS. 1D and 1E, electrical schematic diagrams illustratevariants of the IEEE 802.3af standard in which 1000 Base T communicationis enabled over a four pair Ethernet cable. Inline Power may be suppliedover two pair or four pair. In FIG. 1D the PD accepts power from a pairof diode bridge circuits such as full wave diode bridge rectifier typecircuits well known to those of ordinary skill in the art. Power maycome from either one or both of the diode bridge circuits, dependingupon whether Inline Power is delivered over Pair 1-2, Pair 3-4 or Pair1-2+Pair 3-4. In the circuit shown in FIG. 1E a PD associated with Pair1-2 is powered by Inline Power over Pair 1-2 and a PD associated withPair 3-4 is similarly powered. The approach used will depend upon the PDto be powered.

In accordance with the IEEE 802.3af standard as presently constituted, aPSE carries out an inline power detection process, and, if successful,an inline power classification process. The detection process attemptsto detect an identity network present at the PD. This is usually a25,000 ohm resistor which is detected by applying a first voltage acrossthe inline power conductors and reading a first current drawn, thenapplying a second, higher voltage and reading a second current drawn. Ifthe detection process measures the resistance as 25,000 ohms, then a PDcapable of accepting inline power pursuant to the IEEE 802.3af standardis present. Otherwise, it is not. If such a PD is present, then underthe IEEE 802.3af standard a classification process is implemented toapply a third voltage and measure a third current drawn. The thirdcurrent drawn characterizes the PD as a member of one of a set of fiveIEEE 802.3af classes. Depending upon the class, up to a certain amountof inline power should be provided to the PD by the PSE.

Inline Power is also available through techniques that are non-IEEE802.3af standard compliant as is well known to those of ordinary skillin the art. The techniques described herein are also generallyapplicable to systems which are not IEEE 802.3af standard compliant.

In many cases where PDs are used, it may be desirable to provide someadditional capacity to classify PDs receiving power from PSEs for atleast the purpose of providing more power than is currently contemplatedunder the IEEE 802.3af standard as well as additional and more precisepower gradations.

SUMMARY OF THE INVENTION

In a wired data telecommunication network power sourcing equipment (PSE)coupled to a powered device (PD) carries out an inline power discoveryprocess to verify that the PD is adapted to receive inline power, then aplurality of classification cycles are carried out to convey a series ofinline power classes back to the PSE. The series of inline power classesmay all be the same, in which case the PD is legacy equipment and isadapted to receive the power level corresponding to that class. If theyare not all the same, information is thus conveyed to the PSE which may,for example, correspond to a specific power level to be applied or toother information.

Other aspects of the inventions are described and claimed below, and afurther understanding of the nature and advantages of the inventions maybe realized by reference to the remaining portions of the specificationand the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent invention and, together with the detailed description, serve toexplain the principles and implementations of the invention.

In the drawings:

FIGS. 1A, 1B, 1C, 1D and 1E are electrical schematic diagrams ofportions of data telecommunications networks in accordance with theprior art.

FIG. 2 is an electrical schematic diagram of a network segment inaccordance with an embodiment of the present invention.

FIG. 3 is a block diagram of a portion of a piece of power sourcingequipment in accordance with an embodiment of the present invention.

FIG. 4 is a block diagram of a portion of a powered device in accordancewith an embodiment of the present invention.

FIG. 5 is an electrical schematic diagram of a diode bridge for use witha powered device in accordance with an embodiment of the presentinvention.

FIGS. 6, 7, 8 and 9 are charts of voltage versus time for variousclassification processes carried out in accordance with embodiments ofthe present invention.

FIG. 10 is an electrical circuit block diagram of a portion of a PD inaccordance with an embodiment of the present invention.

FIGS. 11 and 12 are process flow diagrams of processes carried out inaccordance with various embodiments of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention described in the following detaileddescription are directed at networks and network devices incorporatinginline power over a wired data telecommunications network. Those ofordinary skill in the art will realize that the detailed description isillustrative only and is not intended to restrict the scope of theclaimed inventions in any way. Other embodiments of the presentinvention, beyond those embodiments described in the detaileddescription, will readily suggest themselves to those of ordinary skillin the art having the benefit of this disclosure. Reference will now bemade in detail to implementations of the present invention asillustrated in the accompanying drawings. Where appropriate, the samereference indicators will be used throughout the drawings and thefollowing detailed description to refer to the same or similar parts.

In the interest of clarity, not all of the routine features of theimplementations described herein are shown and described. It will, ofcourse, be appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions must be madein order to achieve the developer's specific goals, such as compliancewith application- and business-related constraints, and that thesespecific goals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

In accordance with conventional implementations of the IEEE 802.3afstandard, a detection process is carried out periodically over a port tosee if an IEEE 802.3af PD is coupled thereto so that inline power may beapplied. Full inline power should never be applied to the conductors ofa port in any significant amount for any significant amount of timeprior to verifying the presence across the conductors of an identitynetwork authorizing the inline power because of fear that a piece ofequipment might not operate in a predictable way if it was not built tocomply with the IEEE 802.3af standard. Where an appropriate identitynetwork is detected, then a classification process is carried out todetermine how much power (current) should be provided to the PD. Oncethis classification process is complete, the power is applied until, forexample, the PD is decoupled from the port. The present inventionleverages this standard and provides an additional capability withoutmaking prior equipment obsolete. In accordance with the presentinvention, the detection process is carried out in the same manner,however, the classification process is carried out more than once by thePSE. If the same result is obtained each time the classification processis carried out, then the PD is treated by the PSE as if it is “legacy”IEEE 802.3af PD equipment, i.e., equipment that is unaware of this newcapability and thus presents the same class every time it is classifiedin a sequence to thus flag itself as a legacy device. The PSE implementsan algorithm that assigns a class during each unique independentclassification cycle in a sequence of cycles, identifies the PD's classresponse upon each classification cycle in the sequence, assembles asequence of classes into a binary (or other symbolic) code representinga specific unique sequence based on the different classes (such as thosedefined under the IEEE 802.3af standard, or otherwise) so that thesequence may be interpreted by software/firmware using a lookup table(or equivalent approach) to identify the PD as a member of a particular“class”. To achieve this the PSE applies the same classification voltageover and over, while the PD may elect to draw the same current from thePSE each time (same class) or a sequence of currents not all of whichare the same (sequence of different class symbols), whereupon the PSEassembles and constructs a sequence of symbols corresponding to the“class” of the PD.

While some of the discussions herein may specify particular voltages andmeasured currents or ranges thereof at which certain actions are to betaken, those of ordinary skill in the art will now realize that suchvoltages and measured currents are not required to practice theinvention and that different ranges, values and numbers of ranges may besubstituted.

A network segment 30 is illustrated in FIG. 2. Network segment 30includes a network device 32 configured as power sourcing equipment(such as a switch or hub, for example) capable of providing inline poweraccording to one or more inline power schemes such as the IEEE 802.3afstandard. Network segment 30 also includes powered device 34 which isconfigured to utilize inline power provided by network device 32. Awired data telecommunications network cable 36 couples network device 32and powered device 34 and has at least two pairs of conductors. One pair38 is illustrated here as the conductor 3-6 pair and the other pairshown here, 40, is illustrated as the conductor 1-2 pair. In accordancewith this configuration pair 3-6 carries the more positive leg of theinline power and pair 1-2 carries the less positive leg of the inlinepower. Additional pairs of conductors may be included as is well knownto those of ordinary skill in the art, however, they are not shown herein order to avoid overcomplicating the disclosure.

PSE block 42 provides inline power to pairs 38 and 40 at network device32 and reads return current from powered device 34. It is shown in moredetail in the block diagram at FIG. 3. Turning to FIG. 3 a PSEcontroller 44 controls the voltage output of a voltage injector 46 andreceives a current indication from current detector 48. Voltage injector46 is capable of a number of voltage outputs such as an idle statevoltage output, an inline power detection voltage level, and othervoltage levels associated with the classification of the powered devicediscussed in more detail below, and a high voltage associated withinline power delivery (typically around −48V DC (direct current)).

FIG. 4 is a block diagram illustrating a powered device PD block 48. PDblock 48 receives the inline power over the wired datatelecommunications network cable 36 as shown in FIG. 2. An optionaldiode bridge circuit 50 may be included as shown in more detail in FIG.5 and discussed in more detail below. Voltage received at nodes 52 (+)and 54 (−) is used to power the powered device 34 via nodes 56 (+) and58 (−) if the powered device meets the requirements for receiving inlinepower. In order to determine if powered device 34 meets thoserequirements, PD block 48 must first present an identity network 64 tothe PSE block 42 over the wired data telecommunications network cable 36so that its ability to utilize inline power may be confirmed. Inaccordance with the IEEE 802.3af standard, the identity network is apredetermined resistance such as a 25,000 ohm resistor. Other identitynetworks may also be used in accordance with other standards ortechniques as is well known to those of ordinary skill in the art. PDController 60 causes a switch 62 to close (or in an equivalent mannerpresents the identity network) coupling the identity network 64 to thewired data telecommunications network cable 36 so that it may bedetected by the PSE block 42 during an inline power detection phase. Atother times the identity network need not be presented and thus switch62 may be open. Switch 62 may be any circuit element capable ofswitching electrical current such as a relay, a solid state relay, adiode, a transistor and the like. Alternatively, switch 62 may beomitted and the identity network 64 presented at all times. In order forPD block 48 to convey to PSE block 42 how much power (i.e., current) itwould like to have provided to it, a current source device 66 (or aplurality of separately addressed current source devices (such as acurrent output DAC) which together form current source device 66) iscontrolled by PD controller 60 to provide certain fixed current valuesacross the wired data telecommunications network cable 36 back to PSEblock 42 where the magnitudes of those currents are detected by currentdetector 48 and conveyed to PSE controller 44. The magnitude and orderof a series of those presented currents drawn from the attached PSE inresponse to application of the classification voltage (in one embodimentthe classification voltage is in a range of greater than about 15 voltsto less than about 20 volts) is used to convey information from PD block48 to PSE block 42. The information conveyed may be, for example, amaximum current desired by the powered device 34 from the network device32, but the present invention may be used to convey any kind ofinformation from the powered device 34 to the network device 32.

Diode bridge 50 is, for example, a conventional full wave bridgerectifier optionally provided to insure that if the wires aremisconnected that the more positive signal will be delivered from inputnodes 68 and 70 to node 52 and the less positive signal will bedelivered to node 54.

In accordance with the present invention, a plurality of classificationcycles are carried out by the PSE block 42 on the PD block 48. Anadvantage of the present invention is that if the PSE block 42 attemptsto repetitively classify a PD block belonging to a “legacy” device whichis unaware of or unable to utilize this new capability, it will simplyrespond the same way each time and the PSE will then be able to verifythat the device is a legacy device. On the other hand, if it respondswith a series of current levels at least one of which is not the same asthe others, then the PSE block 42 will be able to verify that thecoupled PD block 48 is capable of supplying the new power classes asdescribed herein.

FIG. 6 illustrates one embodiment of the present invention. Inaccordance with this embodiment, the voltage applied by the PSE block 42to a port connector at the network device 32 (to which cable 36 isattached) is shown as the voltage trace 72 in the graph of voltageversus time. The voltage starts 72(1) at an idle level which inaccordance with the IEEE 802.3af standard is typically a value in arange of about 0.0 VDC to about 2.8 VDC. The voltage is occasionallyramped up 72(2) to a level within a detection range and the returncurrent is measured at one or more voltages (typically two separatevoltages). While this is going on, an inline power compatible PD block48 is presenting its identity network so that the interaction of thatidentity network with the applied voltage can be measured by PSE block42 (typically as a measured current). In accordance with an embodimentof the present invention, the applied voltage is then ramped up to aclassification range 72(4) (it may go through the idle range first tocause a reset at the powered device 72(3)). As shown in FIG. 6 thisoccurs three times, although any number greater than one is consideredto be within the scope of the present invention. As the applied voltagesettles in the classification range the PD block 48 via its controller60 and current source device 66 provides an output current. This outputcurrent is, in accordance with an embodiment of the present invention, acurrent level corresponding to a predetermined measured resistance anddevice class such as one of the power classes specified in the IEEE802.3af standard. The present invention also allows the use of differentor additional measured current levels in addition to those presentlyspecified in the IEEE 802.3af standard. As a result, after a number ofcycles of applying a classification voltage followed by dropping out ofthe classification range the PSE block 42 will have obtained a sequenceof current values which may correspond to power classes. After Nclassification cycles, each of which could return one of M possiblemeasured currents, the PD block 48 thereby conveys to the PSE block 42one of M^(N) (M to the power of N) sequences or codes, corresponding toup to log₂ (M^(N)) bits of information. This sequence or code can beused to tell the PSE block 42 to allocate and provide up to a certainamount of power (current) via inline power to powered device 34, or canbe used for any other purpose. Since more than four conductors may becoupled between network device 32 and powered device 34, this processmay take place on two or more pairs of conductors and affect powerdelivery over whatever conductors are desired. Where four pairs ofconductors couple a network device to a powered device a classificationprocess as described could take place on two pairs and control powerdelivery over all four pairs, and the like. Also note that multipleclassification cycles may take place on both sets of pairs in the cablein an alternating fashion, i.e., if power were to be supplied down fourpairs of conductors, it is feasible and within the scope of the presentinvention to use a first pair of the pairs of conductors (fourconductors) to carry out a first classification, then alternate andcarry out a classification on the second pair of pairs. This isparticularly useful in conjunction with the wiring option illustrated inFIG. 1D where a diode bridge arrangement couples all four pairs. Thiscan achieve two goals: first, it can get a specific sequence to identifythe PD using multiple classification cycles; second, it can insure thatall pairs in the cable are coupled to the same device.

In the embodiment illustrated in the chart of FIG. 6 the applied voltagerises into the classification voltage range (approximately 17 VDC in theIEEE 802.3af standard) and then shifts to a marker level which, in oneembodiment of the present invention, is a voltage level less than theclassification voltage level and above the reset logic voltage level,e.g., 9 VDC. It need not shift down and could, instead, shift up to amarker level that is at a voltage level above the classification voltagelevel, e.g., about 25 VDC. This approach is illustrated in the chart ofFIG. 8. While the applied voltage is in the specified classificationvoltage range the PD block 48 will return a current, when it leaves thatrange (either by increasing or decreasing) it will stop returning thecurrent signal and prepare to return the next current signal.

FIG. 7 is a PD voltage versus time chart illustrating an embodiment ofthe present invention. In accordance with this embodiment, V1 is theidle level voltage, V3 is the classification voltage, V2 is the markervoltage outside of the classification voltage range to which the signalramps between classification cycles. t1 is the ramp time to go from V1to V3 (and vice versa), t2 is the period of time that the voltage staysin the classification range, t3 is the period of time for the voltage toramp from the classification voltage level to the marker level, t4 isthe dwell time at the marker level, t5 is the ramp time from the markerlevel back to the classification level. In an embodiment of the presentinvention (and many other values are possible for these variables andintended to be within the scope of the present invention), t1 is between1 and 4 mSec, t2 is between 10 and 25 mSec, t3 is between 0.13 and 7mSec, t4 is between 5 and 10 mSec, t5 is between 0.13 and 7 mSec and t6(the time to accomplish the entire classification using threeclassification cycles) is between 47 and 155 mSec and preferably lessthan or equal to about 75 mSec. V1 is in a range of about 0.0 VDC toabout 2.8 VDC; V2 is in a range of about 7.5 to about 9.5 VDC; and V3 isin a range of about 15.5 to about 20.5 VDC. When the applied voltage isin a range of between about 2.8 VDC and about 5.0 VDC a state reset willoccur at the PD block 48 causing it to go back and wait for the firstclassification cycle. Those of ordinary skill in the art will nowappreciate that the timing values may be set to any convenient valuesand the voltage values and ranges need not be those exact values andranges set forth above.

FIG. 9 illustrates the operation of another embodiment of the presentinvention. In this case the PSE is a legacy IEEE 802.3af PSE. Suchdevices can normally be requested to initiate a classification cycleeither by application of an electrical signal or by a software/firmwarecommand. In accordance with this embodiment of the invention, the legacyPSE would do a detect and classification cycle as shown in FIG. 9. Atthe end of its first classification cycle, the applied voltage dropsbelow the logic reset threshold and into the idle range. In this case,however, a non-legacy PD is provided and it incorporates a nonvolatilememory (NVM) which may be of the charge storage type or of the typesustained by power stored in a capacitor-like circuit component. In thismanner the fact that a first classification has taken place is not lostby the PD and it may now provide its second classification responsewithout resetting despite the fact that the applied voltage has droppedbelow the logic reset threshold at least for a short period of time.

Next, a software/firmware modification to the legacy PSE causes it tostore a representation of the first classification result in a memoryand then initiate one or more additional subsequent classificationcycles.

When all classification cycles are complete, the last result (which mayor may not be intermediately stored in a memory) is combined with thepreviously stored result values to come up with a classification codeword which can then be used to look up the action to take (such asapplying a certain maximum level of inline power).

In the case of capacitor powered memory, the logic circuit at the PDwill be cleared when the memory capacitor is discharged by dropping theapplied PSE voltage below a certain threshold for a long enough periodof time, e.g., 0.5 second or thereabout due to the discharging effect ofthe capacitor through the identity network or other circuitry such as acurrent source. A clear-memory signal can be transmitted to erase acharge-based NVM-type memory (e.g., EEPROM (electrically eraseableprogrammable read only memory)), if used. The high voltages needed bysuch memories can be supplied by conventional charge pumps.

In order to insure that the voltage on the PD capacitor (a capacitorcoupled in parallel with the identity network and forming an RC circuitwith it) can decrease to the PSE-applied voltage within a reasonableperiod of time, active discharge may be used. This may be implemented atthe PSE by using a current source to drain the PD capacitor over theconductors. This may also be implemented at the PD as illustrated inschematic/block diagram form in FIG. 10. In FIG. 10 the identitynetwork, PD electronics, C_(PD) and current source I_(CLASS) are allcoupled between the two conductors at nodes 51 and 54. Current sourceI_(CLASS) is used to report the classification current. C_(PD) is the PDcapacitor mentioned above (typically about 0.1 uF). Current sourceI_(MEM) is used to feed a portion of the available current to thecapacitor-based nonvolatile memory capacitor C_(MEM). Resistor R_(MEM)is selected to discharge capacitor C_(MEM) in a reasonable amount oftime. Zener diode Z_(MEM) is used to set the value of the voltage acrossC_(MEM), i.e., the supply voltage for the memory.

Active discharge entails turning on a current source 74 at the PD todischarge the PD capacitor 76. This current source can be made activewhen the voltage across the capacitor 76 exceeds the voltage applied tothe PD from the PSE.

The IEEE 802.3af standard defines five power classes which correspond tocertain currents returned by the PD to the PSE during a classificationcycle. These are set forth in Table I: TABLE I PSE ClassificationCorresponding Class Current Range (mA) Inline Power Level (W) 0 0-5 15.41  8-13 4.0 2 16-21 7.0 3 25-31 15.4 4 35-45 15.4

By adapting this scheme to a plural classification system, a 30 W powerlevel could be defined, for example, with a 3-0-3 or a 0-3-0; a 40 Wpower level could be defined, for example, with a 2-0-2, and the like.Where additional classification is required, additional current classesmay be added to the basic IEEE 802.3af specification, e.g. as set forthin TABLE II: TABLE II PSE Classification Corresponding Class CurrentRange (mA) Inline Power Level (W) 5 51-61 Not presently defined by thestandard.Note that in accordance with the IEEE 802.3af standard, if a currentmuch higher than about 70-80 mA and less than about 100 mA is detectedduring a classification cycle, especially at the beginning of theclassification cycle, the PSE will process this as an over current faultand no more classification cycles will take place in order to avoiddamage. The PSE may or may not continue with classification cycles toattempt to power such a PD. Non-IEEE . . . 802.3af standard compliantsystems need not incorporate this limitation.

Accordingly, sequences of identical values would simply continue torepresent the value corresponding to the identical value, e.g., 0-0-0would represent Class 0, and the like. Mixed values would be defined, aswith a lookup table, to represent other values and/or other actions tobe taken. For example, where it is desirable to be extremely precise inthe amount of power allocated, different power levels could be assignedto different sequences, so with 6 possible classes (0-5) and threepositions there would be 210 minor classes available for use in additionto the 6 major classes. If even more are desired, a fourth or fifth (ormore) classification cycle can be added as can additional classes.Additionally, a specific code, e.g., 5-5-4 could be defined to specify,for example, that an additional sequence of current values is to be readin addition to the initial three, e.g., 5-5-4-1-2-3-4-5. Such a codingsystem may now be used to convey information in addition to desiredpower levels. For example, a Voice Over Internet Protocol (VOIP)telephone configured as a powered device could be programmed totemporarily break its connection with the PSE port to force the PSE tore-classify it (disruption of the inline power current draw will causesuch a reset) and then, upon reclassification, it could send a message.The message could take any form, such as to cause the switch to send analert to someone, such as a security official in response to a panicbutton associated with the telephone being depressed, or, if atemperature or other environmental sensor were included in thetelephone, it could report an anomalous condition sensed by that sensor,such as a fire, or the like, via the switch to an appropriate recipient.

Because the PD is, by definition, a powered device and does not receiveany power until inline power is applied, it needs to have some power inorder to carry out the interactions described herein with the PSE. Thismay be as simple as charging a capacitor to power its internal circuitrywhile it is coupled to the PSE and receiving either the idle currentsignal, an intermediate signal and/or the classification voltage signal.To charge its capacitor, the PD may choose to use a fraction of thecurrent it draws from the PSE during its first classification cycle. Thecharge on the capacitor helps the PD keep its low power memory alive sothat the right sequence can be presented to the PSE as moreclassification cycles occur. Its current source device 66 is adapted tooperate on the applied power from the PSE during the classificationphase. Avoiding dropping the idle current to zero can avoid a situationwhere the PD would forget where it was in the classification process andreset. It will reset if the voltage drops into the region denoted 72(3)in FIG. 6.

Turning now to FIG. 11, a process flow diagram illustrates the processflow 100 from the PSE side of the connection in accordance with anembodiment of the present invention. The process starts at block 102. Atblock 104 the PSE attempts to discover the PD by carrying out adetection process aimed at verifying the presence of an appropriateidentity network disposed across the conductors of the wired datatelecommunications network. If no identity network is found (block 106),control reverts back to block 104 to continue the detection process fromtime to time until an identity network is found. If an identity networkis found, control passes to block 108 where the classification processstarts. As discussed above, the classification process involves aplurality of cycles into and out of a classification voltage range(block 110) while reading the return current while in the classificationvoltage range (block 112). If an overcurrent condition ever exists, thecontrol should revert to the beginning at block 102 to immediately avoidthe overcurrent condition (block 114). In an embodiment of the presentinvention the overcurrent monitoring is performed at the PSE and not atthe PD. Each measured current corresponds to a “class” such as the IEEEclasses described above, or other classes defined in a non-IEEE 802.3afstandard system. These classes are determined (block 116) by correlatingthe measured current with a class value or other representation. Thismay be done in one embodiment of the invention, by a lookup table orother software/firmware implementation which yields a class value inresponse to the measured current. The collection of classes thusdetermined are kept while other classification cycles are performed(block 118, block 120) and together these classes determine the sequenceof classes assembled and stored in controller 44 of FIG. 3 as a binary(or other symbolic) code word, allowing the software/firmware to accesscontroller 44 and, using a lookup table or similar approach, carry outthe proper function, e.g., determine the resulting classification (block122) and provide inline power until interrupted (block 124) and onceinterrupted, return to start.. As discussed above, the informationcontained in the classification can result in the allocation of acertain corresponding power level to the PD or may mean something elsesuch as a measured environmental condition, or the like. The PSE acts onthe determined result, accordingly.

Turning now to FIG. 12, a process flow diagram illustrates the processflow 130 from the PD side of the connection in accordance with anembodiment of the present invention. The process starts at block 132. Atblock 134 the PD presents its identity network across the conductors ofthe wired data telecommunications network (e.g., across two pairs). Theidentity network may be a 25,000 ohm resistance if the PD is IEEE802.3af standard compliant. The identity network may be presented inresponse to a detection by the PD of the idle voltage level (or simplybe present at all times). At block 136, the voltage applied by the PSE(“VPD”) rises to carry out the detection of the identity network, dropsinto the idle range to force a reset of the PD, and raises into theclassification range for the first time. In block 138 when the appliedvoltage from the PSE reaches the classification range the PD draws itsfirst classification current on the wired data telecommunicationsnetwork cable. At block 142 when the VPD departs the classificationvoltage range (either by going up or by going down, but not by goinginto the state reset or idle voltage ranges) then the PD presents itsnext class current. At block 144 if the VPD continues to drop into thereset logic or idle levels then the PSE is a legacy PSE and the PD knowsthat it can only receive inline power corresponding to its first classresponse and that no further inline power classification may take place.Control transfers from block 144 to block 146A where the PD operates asa legacy PD receiving inline power until some other condition appears.Also, a PD may see a continuing loop of detection and classification fora limited an unbounded amount of time, (e.g., the PSE cannot supplypower at this time) in such a case, if a legacy IEEE 802.3af PSE isattached, the PD will repeatedly present its 25,000 ohm identity networkfollowed by the first class in its sequence since its logic gets resetupon a new detection cycle or upon entering its own logic resetthreshold on the way down to the 2.8 VDC voltage level required to bereached at the end of a detection cycle. At block 148 the second currentin sequence is presented when the VPD is in classification range. Atblock 150 the third (and there may be more of these) classification ispresented when the VPD is in classification range. Then controltransfers to block 146B where the inline power level requested in themulti-cycle classification process is provided to power the PD untilinterrupted. If power is interrupted, control transfers back to thestart (block 132) and the PD presents its first class in response to aclassification cycle by the PSE.

Note that any number of cycles may be carried out, as appropriate to theparticular application. Also note that the PD could be configured tocontinue presenting various values each time it is classified until theVPD drops into the state reset range.

It should be noted that while certain circuitry has been shown in theconfigurations of the PSE/PD ports, any circuitry suitable to carry outthe functions specified may be used and the implementation of suchcircuitry in any number of various forms is well within the skill ofthose of ordinary skill in the art having the benefit of thisdisclosure. It should also be noted that while in several contexts the“disruption” of power and/or data to a port of a network device has beendiscussed as a precursor to a switching event to reconstitute dataand/or power over wired network service to a particular port, thedisruption or the switching event in the absence of a disruption couldbe caused by a command to the network device from a control point suchas a master control center or other control location, a hardware orsoftware failure, deliberate (or inadvertent) de-powering of a device,or from any other cause.

In accordance with an embodiment of the present invention, ahigh-security device such as a telephone or camera receiving inlinepower over a wired data telecommunication network could be configured tonot receive inline power if it was receiving inline power and that powerwas temporarily interrupted. A cable failure or unplug/replug cyclecould cause this and under certain circumstances it would be desirableto require a confirmatory act such as operator intervention and/orpassword entry into a computer device on the wired datatelecommunications network before resupplying the inline power. Such afailure could also trigger an alarm or message to an appropriate networkcontrol point.

In accordance with another embodiment of the present invention, a PDcould present a sequence of power classes that assemble into a codewordmeaning “data and/or power redundancy are required”, “power over 4 pairsof conductors is required”, and the like. Similarly, a device mightsignal that it is a “high-priority” device and, as such, should be givenpriority in inline power so that if there is a shortage of inline poweravailable, power should be given up by other devices to power thepriority device.

In accordance with an embodiment of the present invention, a securitymessage may be sent from the PD to the PSE as follows: (1) interruptinga flow of inline power between the PSE and the PD at the PD in responseto a security alert input (such as a manual input like a switch closureor a sensor-based input like a temperature sensor limit crossing or thelike); (2) initiating an inline power discovery cycle in response tosaid interrupting; and (3) presenting at the PD, in response to thesecurity alert input and said initiating, an identification networkcorresponding to the security message. In this case the identity networkwould be different from, for example, the IEEE 802.3af standard 25,000ohm resistance—say 30,000 ohms or 15,000 ohms, or the like. In responseto receipt of the security message at the PSE an alarm could be sounded,a message could be forwarded, or the like.

In accordance with another embodiment of the present invention, asecurity message may be sent from the PD to the PSE as follows: (1)interrupting a flow of inline power between the PSE and the PD at the PDin response to a security alert input (such as a manual input like aswitch closure or a sensor-based input like a temperature sensor limitcrossing or the like); (2) initiating an inline power discovery cycle inresponse to said interrupting; (3) discovering that the PD is adapted toreceive inline power from the PSE; (4) conducting a plurality of inlinepower classification cycles, each comprising: applying a classificationvoltage to the conductors; measuring current in the conductors while theclassification voltage is applied; and determining a class correspondingto the measured current; (5) combining the plurality of classesdetermined into a classification code for the PD; and (6) determiningthat the classification code corresponds to a predetermined securitymessage. In response to receipt of the security message at the PSE analarm could be sounded, a message could be forwarded, or the like.

In accordance with another embodiment of the present invention, apriority message may be sent from the PD to the PSE in order to get ahigh priority allocation of available (or previously assigned) inlinepower resources, as follows: (1) interrupting a flow of inline powerbetween the PSE and the PD at the PD in response to a security alertinput; (2) initiating an inline power discovery cycle in response tosaid interrupting; and (3) presenting at the PD, in response to thesecurity alert input and said initiating, an identification networkcorresponding to the request for priority.

In accordance with another embodiment of the present invention, apriority message may be sent from the PD to the PSE in order to get ahigh priority allocation of available (or previously assigned) inlinepower resources, as follows: (1) interrupting a flow of inline powerbetween the PSE and the PD at the PD in response to request for priorityinput; (2) initiating an inline power discovery cycle in response tosaid interrupting; (3) discovering that the PD is adapted to receiveinline power from the PSE; (4) conducting a plurality of inline powerclassification cycles, each comprising: applying a classificationvoltage to the conductors; measuring current in the conductors while theclassification voltage is applied; and determining a class correspondingto the measured current; (5) combining the plurality of classesdetermined into a classification code for the PD; and (6) determiningthat the classification code corresponds to a request for priority.

While embodiments and applications of this invention have been shown anddescribed, it will now be apparent to those skilled in the art havingthe benefit of this disclosure that many more modifications thanmentioned above are possible without departing from the inventiveconcepts disclosed herein. Therefore, the appended claims are intendedto encompass within their scope all such modifications as are within thetrue spirit and scope of this invention.

1. A method for classifying a powered device (PD) coupled to powersourcing equipment (PSE) to receive inline power from the PSE in a wireddata telecommunications network having at least two pairs of conductorscoupling the PD and the PSE, the method comprising: discovering that thePD is adapted to receive inline power from the PSE; conducting aplurality of classification cycles, each comprising: applying aclassification voltage to the conductors; measuring the current in theconductors while the classification voltage is applied; and determininga class responsive to the measured current.
 2. The method of claim 1,wherein the classification voltage is a voltage in a range of about 15volts DC (direct current) to about 20 volts DC.
 3. The method of claim1, further comprising: combining the plurality of classes determinedinto a classification code for the PD; and taking an action in responseto the classification code.
 4. The method of claim 3, wherein saidtaking an action includes applying inline power as specified by theclassification code.
 5. The method of claim 3, wherein said taking anaction includes: conducting at least one additional classificationcycle, the at least one additional classification cycle comprising:applying a classification voltage to the conductors; measuring thecurrent in the conductors while the classification voltage is applied;and determining a class responsive to the measured current.
 6. Themethod of claim 1, further comprising: applying, in response todetermining that the power class for each of the plurality ofclassification cycles is the same, inline power corresponding to thatpower class.
 7. The method of claim 1, wherein said determining a classincludes: using a look up table indexed by measured current value todetermine a class responsive to the measured current value.
 8. Themethod of claim 1, further comprising: initiating said conducting inresponse to a command.
 9. The method of claim 1, further comprising:initiating said conducting in response to interruption of inline powerdelivery from the PSE to the PD.
 10. The method of claim 1, furthercomprising: storing in nonvolatile memory at the PD a representationthat a classification procedure is underway, the nonvolatile memoryadapted to store information for a period of time in the absence ofinline power voltage exceeding a reset logic level.
 11. The method ofclaim 10, wherein the nonvolatile memory is powered by a capacitordisposed at the PD, the capacitor drawing charge from voltage applied tothe conductors.
 12. The method of claim 11, further comprising: droppinga voltage signal applied to the conductors during the conducting of theplurality of classification cycles below a reset logic level betweenclassification cycles.
 13. The method of claim 12, further comprising:combining the plurality of classes determined into a classification codefor the PD; and taking an action in response to the classification code.14. The method of claim 3, wherein during the conducting of theplurality of classification cycles, a voltage applied to the PD by thePSE ramps to a marker level voltage between classification cycles, themarker level voltage being outside the classification voltage range andabove a reset logic level for the PD.
 15. The method of claim 1, furthercomprising: monitoring the current drawn by the PD over the conductorsand, if it exceeds a predetermined level during said conducting,terminating said conducting.
 16. The method of claim 1, wherein theconductors comprise two pairs of conductors.
 17. The method of claim 1,wherein the conductors comprise four pairs of conductors.
 18. The methodof claim 17, wherein said conducting is carried out over two pairs ofthe four pairs of conductors.
 19. The method of claim 17, wherein saidconducting is carried out over all pairs of the four pairs ofconductors.
 20. An apparatus for classifying a powered device (PD)coupled to power sourcing equipment (PSE) to receive inline power fromthe PSE in a wired data telecommunications network having at least twopairs of conductors coupling the PD and the PSE, the apparatuscomprising: means for discovering that the PD is adapted to receiveinline power from the PSE; means for conducting a plurality ofclassification cycles, each comprising: applying a classificationvoltage to the conductors; measuring the current in the conductors whilethe classification voltage is applied; and determining a classresponsive to the measured current.
 21. The apparatus of claim 20,wherein the classification voltage is a voltage in a range of about 15volts DC (direct current) to about 20 volts DC.
 22. The apparatus ofclaim 20, further comprising: means for combining the plurality ofclasses determined into a classification code for the PD; and means fortaking an action in response to the classification code.
 23. Theapparatus of claim 22, wherein said means for taking an action includesmeans for applying inline power as specified by the classification code.24. The apparatus of claim 22, wherein said means for taking an actionincludes means for conducting at least one additional classificationcycle, the at least one additional classification cycle comprising:applying a classification voltage to the conductors; measuring thecurrent in the conductors while the classification voltage is applied;and determining a class responsive to the measured current.
 25. Theapparatus of claim 20, further comprising: means for applying, inresponse to means for determining that the power class for each of theplurality of classification cycles is the same, inline powercorresponding to that power class.
 26. The apparatus of claim 20,wherein said means for determining a class includes: means for using alook up table indexed by measured current value to determine a classresponsive to the measured current value.
 27. The apparatus of claim 20,further comprising: means for initiating said means for conducting inresponse to a command.
 28. The apparatus of claim 20, furthercomprising: means for initiating said conducting in response tointerruption of inline power delivery from the PSE to the PD.
 29. Theapparatus of claim 20, further comprising: means for storing innonvolatile memory at the PD a representation that a classificationprocedure is underway, the nonvolatile memory adapted to storeinformation for a period of time in the absence of inline power voltageexceeding a reset logic level.
 30. The apparatus of claim 29, whereinthe nonvolatile memory is powered by a capacitor disposed at the PD, thecapacitor drawing charge from voltage applied to the conductors.
 31. Theapparatus of claim 30, further comprising: means for dropping a voltagesignal applied to the conductors during the conducting of the pluralityof classification cycles below a reset logic level betweenclassification cycles.
 32. The apparatus of claim 31, furthercomprising: means for combining the plurality of classes determined intoa classification code for the PD; and means for taking an action inresponse to the classification code.
 33. The apparatus of claim 22,wherein during the conducting of the plurality of classification cycles,a voltage applied to the PD by the PSE ramps to a marker level voltagebetween classification cycles, the marker level voltage being outsidethe classification voltage range and above a reset logic level for thePD.
 34. The apparatus of claim 20, further comprising: means formonitoring the current drawn by the PD over the conductors and, if itexceeds a predetermined level during said conducting, terminating saidconducting.
 35. The apparatus of claim 20, wherein the conductorscomprise two pairs of conductors.
 36. The apparatus of claim 20, whereinthe conductors comprise four pairs of conductors.
 37. The apparatus ofclaim 36, wherein said means for conducting utilizes two pairs of thefour pairs of conductors.
 38. The apparatus of claim 36, wherein saidmeans for conducting utilizes all pairs of the four pairs of conductors.39. A system for classifying a powered device (PD) coupled to powersourcing equipment (PSE) to receive inline power from the PSE in a wireddata telecommunications network having at least two pairs of conductorscoupling the PD and the PSE, the system comprising: circuitry fordiscovering that the PD is adapted to receive inline power from the PSE;circuitry for conducting a plurality of classification cycles, eachcomprising: applying a classification voltage to the conductors;measuring the current in the conductors while the classification voltageis applied; and determining a class responsive to the measured current.40. The system of claim 39, wherein the classification voltage is avoltage in a range of about 15 volts DC (direct current) to about 20volts DC.
 41. The system of claim 39, further comprising: circuitry forcombining the plurality of classes determined into a classification codefor the PD; and circuitry for taking an action in response to theclassification code.
 42. The system of claim 41, wherein said circuitryfor taking an action includes circuitry for applying inline power asspecified by the classification code.
 43. The system of claim 41,wherein said circuitry for taking an action includes circuitry forconducting at least one additional classification cycle, the at leastone additional classification cycle comprising: applying aclassification voltage to the conductors; measuring the current in theconductors while the classification voltage is applied; and determininga class responsive to the measured current.
 44. The system of claim 39,further comprising: circuitry for applying, in response to circuitry fordetermining that the power class for each of the plurality ofclassification cycles is the same, inline power corresponding to thatpower class.
 45. The system of claim 39, wherein said circuitry fordetermining a class includes: circuitry for using a look up tableindexed by measured current value to determine a class responsive to themeasured current value.
 46. The system of claim 39, further comprising:circuitry for initiating said means for conducting in response to acommand.
 47. The system of claim 39, further comprising: circuitry forinitiating said conducting in response to interruption of inline powerdelivery from the PSE to the PD.
 48. The system of claim 39, furthercomprising: circuitry for storing in nonvolatile memory at the PD arepresentation that a classification procedure is underway, thenonvolatile memory adapted to store information for a period of time inthe absence of inline power voltage exceeding a reset logic level. 49.The system of claim 48, wherein the nonvolatile memory is powered by acapacitor disposed at the PD, the capacitor drawing charge from voltageapplied to the conductors.
 50. The system of claim 49, furthercomprising: circuitry for dropping a voltage signal applied to theconductors during the conducting of the plurality of classificationcycles below a reset logic level between classification cycles.
 51. Thesystem of claim 50, further comprising: circuitry for combining theplurality of classes determined into a classification code for the PD;and circuitry for taking an action in response to the classificationcode.
 52. The system of claim 41, wherein during the conducting of theplurality of classification cycles, a voltage applied to the PD by thePSE ramps to a marker level voltage between classification cycles, themarker level voltage being outside the classification voltage range andabove a reset logic level for the PD.
 53. The system of claim 39,further comprising: circuitry for monitoring the current drawn by the PDover the conductors and, if it exceeds a predetermined level during saidconducting, terminating said conducting.
 54. The system of claim 39,wherein the conductors comprise two pairs of conductors.
 55. The systemof claim 39, wherein the conductors comprise four pairs of conductors.56. The system of claim 55, wherein said circuitry for conductingutilizes two pairs of the four pairs of conductors.
 57. The system ofclaim 55, wherein said circuitry for conducting utilizes all pairs ofthe four pairs of conductors.
 58. A program storage device readable by amachine, tangibly embodying a program of instructions executable by themachine to perform a method for classifying a powered device (PD)coupled to power sourcing equipment (PSE) to receive inline power fromthe PSE in a wired data telecommunications network having at least twopairs of conductors coupling the PD and the PSE, the method comprising:discovering that the PD is adapted to receive inline power from the PSE;conducting a plurality of classification cycles, each comprising:applying a classification voltage to the conductors; measuring thecurrent in the conductors while the classification voltage is applied;and determining a class responsive to the measured current.
 59. Themethod of claim 3, wherein said taking an action includes the sensing ofan event at the PD.
 60. The method of claim 59, wherein the eventcorresponds to the activation of a switch.
 61. The method of claim 59,wherein the event corresponds to the measurement of an environmentalvalue with a sensor.
 62. The method of claim 59, further comprising:disrupting an existing connection between the PD and the PSE in order tocause the initiation of the discovering.
 63. Power Sourcing Equipment(PSE) adapted to classify a coupled powered device (PD) so that it canreceive inline power from the PSE in a wired data telecommunicationsnetwork having at least two pairs of conductors coupling the PD and thePSE, the PSE comprising: circuitry for discovering that a coupled PD isadapted to receive inline power from the PSE; circuitry for conducting aplurality of classification procedures, each procedure comprising:applying a classification voltage to the conductors; measuring thecurrent in the conductors while the voltage is applied; and determiningan inline power class responsive to the measured current; and circuitryfor providing a level of inline power responsive to the plurality ofinline power classes determined.
 64. The PSE of claim 63, wherein thecircuitry for conducting a plurality of classification proceduresincludes a lookup table stored in a memory to determine an inline powerclass associated with the measured current value.
 65. The PSE of claim63, wherein the circuitry for conducting a plurality of classificationprocedures includes a lookup table stored in a memory to determine thelevel of inline power to be provided to the PD in response to theplurality of inline power classes presented.
 66. A powered device (PD)adapted to operate in conjunction with a coupled power sourcingequipment (PSE) so that it can receive inline power from the PSE in awired data telecommunications network having at least two pairs ofconductors coupling the PD and the PSE, the PD comprising: an identitynetwork responsive to a signal from the PSE for confirming that the PDis adapted to receive inline power from the PSE; circuitry responsive toa series of classification cycles carried out by the PSE, the circuitrypresenting a series of responsive currents over the conductors to thePSE, the currents corresponding to predetermined inline power classesand the classes not all being the same.
 67. The PD of claim 66, furthercomprising: a nonvolatile memory capable of retaining its contents forat least a period of time while a voltage signal from the PSE dropsbelow a predetermined voltage.
 68. The PD of claim 67, furthercomprising: a current source circuit for maintaining a voltage at the PDat a level no greater than that of the voltage signal applied by thePSE.
 69. The PD of claim 67, wherein said nonvolatile memory is poweredby a capacitor disposed at the PD.
 70. The PD of claim 67, wherein saidnonvolatile memory is based upon stored electrical charge and requiresno external power to hold its contents.
 71. The method of claim 1,wherein said determining a class includes: using a look up table indexedby the plurality of measured current values to determine a classresponsive to the plurality of measured current values.
 72. Theapparatus of claim 20, further comprising: means for using a look uptable indexed by the plurality of measured current values to determine aclass responsive to the plurality of measured current values.
 73. Thesystem of claim 39, further comprising: circuitry for using a look uptable indexed by the plurality of measured current values to determine aclass responsive to the plurality of measured current values.
 74. Amethod for sending a security message from a powered device (PD)receiving inline power from and coupled to power sourcing equipment(PSE) in a wired data telecommunications network having at least twopairs of conductors coupling the PD and the PSE, the method comprising:interrupting a flow of inline power between the PSE and the PD at the PDin response to a security alert input; initiating an inline powerdiscovery cycle in response to said interrupting; and presenting at thePD, in response to the security alert input and said initiating, anidentification network corresponding to the security message.
 75. Amethod for sending a security message from a powered device (PD)receiving inline power from and coupled to power sourcing equipment(PSE) in a wired data telecommunications network having at least twopairs of conductors coupling the PD and the PSE, the method comprising:interrupting a flow of inline power between the PSE and the PD at the PDin response to a security alert input; initiating an inline powerdiscovery cycle in response to said interrupting; discovering that thePD is adapted to receive inline power from the PSE; conducting aplurality of inline power classification cycles, each comprising:applying a classification voltage to the conductors; measuring currentin the conductors while the classification voltage is applied;determining a class corresponding to the measured current; combining theplurality of classes determined into a classification code for the PD;and determining that the classification code corresponds to apredetermined security message.
 76. A method in accordance with claim74, further comprising: sounding an alarm responsive to the receipt ofthe security message.
 77. A method in accordance with claim 75, furthercomprising: sounding an alarm responsive to the receipt of the securitymessage.
 78. A method in accordance with claim 74, further comprising:forwarding an alarm message in response to the receipt of the securitymessage.
 79. A method in accordance with claim 75, further comprising:forwarding an alarm message in response to the receipt of the securitymessage.
 80. A method in accordance with claim 74, wherein: the securitymessage is manually initiated.
 81. A method in accordance with claim 75,wherein: the security message is manually initiated.
 82. A method inaccordance with claim 74, wherein: the security message is automaticallyinitiated in response to a sensor output.
 83. A method in accordancewith claim 75, wherein: the security message is automatically initiatedin response to a sensor output.
 84. A method for sending a request forpriority from a powered device (PD) receiving inline power from andcoupled to power sourcing equipment (PSE) in a wired datatelecommunications network having at least two pairs of conductorscoupling the PD and the PSE, the method comprising: interrupting a flowof inline power between the PSE and the PD at the PD in response to asecurity alert input; initiating an inline power discovery cycle inresponse to said interrupting; and presenting at the PD, in response tothe security alert input and said initiating, an identification networkcorresponding to the request for priority.
 85. A method for sending arequest for priority from a powered device (PD) receiving inline powerfrom and coupled to power sourcing equipment (PSE) in a wired datatelecommunications network having at least two pairs of conductorscoupling the PD and the PSE, the method comprising: interrupting a flowof inline power between the PSE and the PD at the PD in response to therequest for priority input; initiating an inline power discovery cyclein response to said interrupting; discovering that the PD is adapted toreceive inline power from the PSE; conducting a plurality of inlinepower classification cycles, each comprising: applying a classificationvoltage to the conductors; measuring current in the conductors while theclassification voltage is applied; determining a class corresponding tothe measured current; combining the plurality of classes determined intoa classification code for the PD; and determining that theclassification code corresponds to a request for priority.
 86. A methodin accordance with claim 84, further comprising: assigning the PDpriority for inline power allocation in response to the receipt of therequest for priority.
 87. A method in accordance with claim 85, furthercomprising: assigning the PD priority for inline power allocation inresponse to the receipt of the request for priority.
 88. A method forimplementing secure power for a powered device (PD) receiving inlinepower from and coupled to power sourcing equipment (PSE) in a wired datatelecommunications network having at least two pairs of conductorscoupling the PD and the PSE, the method comprising: initiating an inlinepower discovery cycle; presenting at the PD to the PSE, anidentification network corresponding to the request for secure power;disconnecting the PD from the PSE; reconnecting the PD to the PSE; andrequiring operator intervention prior to again providing inline powerfrom the PSE to the PD that requested secure power.
 89. The method ofclaim 88, wherein the operator intervention requires entry of a passwordinto a computer device coupled to the wired data telecommunicationsnetwork.
 90. The method of claim 89, wherein the identification networkcomprises a resistance outside the range specified in the IEEE 802.3afstandard for inline power discovery.
 91. A method for implementingsecure power for a powered device (PD) receiving inline power from andcoupled to power sourcing equipment (PSE) in a wired datatelecommunications network having at least two pairs of conductorscoupling the PD and the PSE, the method comprising: initiating an inlinepower discovery cycle; discovering that the PD is adapted to receiveinline power from the PSE; conducting a plurality of inline powerclassification cycles, each comprising: applying a classificationvoltage to the conductors; measuring current in the conductors while theclassification voltage is applied; and determining a class correspondingto the measured current; combining the plurality of classes determinedinto a classification code for the PD; determining that theclassification code corresponds to a request for secure power; andconfiguring the PSE in response to said determining to refuse to provideinline power again to the PD if inline power is interrupted to the PDwithout first requiring operator intervention.
 92. A method inaccordance with claim 91, wherein the operator intervention requiresentry of a password into a computer device coupled to the wired datatelecommunications network.
 93. A method for implementing 4-conductorpair power for a powered device (PD) receiving inline power from andcoupled to power sourcing equipment (PSE) in a wired datatelecommunications network having four pairs of conductors coupling thePD and the PSE, the method comprising: initiating an inline powerdiscovery cycle; presenting at the PD to the PSE, an identificationnetwork corresponding to a request for 4-conductor pair power; andconfiguring the PSE in response to said determining to provide4-conductor inline power to the PD.
 94. The method of claim 93, whereinthe identification network comprises a resistance outside the rangespecified in the IEEE 802.3af standard for inline power discovery.
 95. Amethod for implementing 4-conductor pair power for a powered device (PD)receiving inline power from and coupled to power sourcing equipment(PSE) in a wired data telecommunications network having at least fourpairs of conductors coupling the PD and the PSE, the method comprising:initiating an inline power discovery cycle; discovering that the PD isadapted to receive inline power from the PSE; conducting a plurality ofinline power classification cycles, each comprising: applying aclassification voltage to the conductors; measuring current in theconductors while the classification voltage is applied; and determininga class corresponding to the measured current; combining the pluralityof classes determined into a classification code for the PD; determiningthat the classification code corresponds to a request for 4-conductorpower; and configuring the PSE in response to said determining toprovide 4-conductor inline power to the PD.